Rectangular to circular waveguide transition



' .7 QEENDERBY v3,349,346

' RECTANGULAR TO CIRCULAR WAVEGUIDE TRANSITION Filed Mgrch a, 1965- 2Shets-Sheet I 20+] 25* FIG. I

' FIG. 20

FIG. 2C

FIG; 28

FIG. 2F

R. N ER BY INVE CHARLES E.

ATTORNEY Oct. 24, 1967 c. E. ENDERBY 3,349,346 RECTANGULAR TO CIRCULARWAVEGUIDE TRANSITION Filed March e, was 2 Sheets-Sheet 2 \NVENTORCHARLES E. ENDERBY ATTORNEY United States Patent Ofifice 3,349,346RECTANGULAR T CIRCULAR WAVEGUIDE TRANSITION Charles E. Enderby, PaloAlto, Calif., assignor to General Electric Company, a corporation of NewYork Filed Mar. 8, 1965, Ser. No. 437,672 3 Claims. (Cl. 333-21)ABSTRACT (IF THE DISCLOSURE A transition device between a rectangularwaveguide having broad and narrow walls of predetermined transverselength and a circular waveguide having a predetermined radius,comprising: a first rectangular portion wherein one narrow wall ischanged to an arcuate narrow wall over a predetermined longitudinallength, said arcuate narrow wall having a radius equal to the radius ofsaid circular waveguide; a second portion of predetermined longitudinallength over which the internal crosssection area is increased bygradually increasing the circumferential length of said arcuate wall bypivoting said broad walls at their junctions with the other narrow wallto thereby form a semicircular cross-section at the end of said secondportion; and a third portion of predetermined longitudinal length overwhich the internal crosssection area is gradually further increased bygradually folding at the center thereof the two halves of the straightwall of said semi-circular cross-section until said two halves coincidein a radially extending knife edge at the end of said third portion, anda radially extending conductive ridge position to substantiallybifurcate the length of the third portion of said transition device,whereby an undesirable TE mode is suppressed.

This invention relates to a rectangular to circular waveguide transitionstructure and more particularly to a structure for providing wide-band,low-loss transition of electromagnetic waves propagating in the TE modein a rectangular waveguide to the TE mode in a circular waveguide andvice versa.

Various structures for providing a transistion between a rectangularwaveguide and a circular waveguide have been proposed. Previouslyproposed transition structures are shown, for example, by F. E. Parisiin U.S. Patent No. 2,825,031, issued Feb. 25, 1958 and by G. R. P. Mariein US. Patent No. 2,859,412, issued Nov. 4, 1958. Other examples aretherein cited.

In general, prior transition structures require configurations that arediflicult and expensive to construct if energy losses and excitation ofundesirable modes are to be avoided. Furthermore, many of the previouslyproposed transition devices involve the intermediate conversion of, forexample, an input rectangular TE mode to a rectangular TE mode, thelatter mode then being converted to the desired circular mode.

It is an object of the present invention to provide a relatively simpleand easily constructed structure 'for efficiently converting arectangular mode to a circular mode.

It is a more specific object of the invention to provide a wide-band,low-loss transition of an electromagnetic wave propagating in the TEmode in a rectangular waveguide to a TE mode for propagation in acircular waveguide.

It is a further object of the invention to prevent the propagation ofundesired modes in a mode conversion structure.

It is another object of the invention to provide smooth and continuoustransition from a given rectangular mode to a given circular modewithout transition to an intermediate rectangular mode.

3,349,346 Patented Oct. 24, 1967 These and other objects are achievedaccording to the present invention by providing a transistion structurein which the internal cross-section area is smoothly altered over apredetermined length from a rectangular shape to a circular shape.

This is accomplished by first forming one narrow wall of the rectangularwaveguide into an arc corresponding to the circumference of the circularwaveguide. Then the broad walls of the rectangular waveguide aregradually flared by pivoting these broad walls at the corners of thestraight narrow wall thus increasing the length of the arcuate narrowWall, until a cross-section of semi-circular shape is obtained. Thesemi-circular cross-section is then formed into the desired circularcross-section by gradually folding the two halves of the straight wallof the semicircular shape toward one another, pivoting at the center ofthis straight wall, until this wall completely disappears.

The illustrated embodiment of the invention provides ease ofconstruction in that the main transition member may be separatelyformed, as for example, by machining from solid stock, and then insertedinto a section of circular waveguide.

To prevent formation and propagation of undesirable modes an elongated,radially positioned conductive ridge may be positioned to bifurcate thewaveguide channel of the transition structure without interference withthe conversion from the rectangular mode to the desired circular mode.

The invention is described more specifically with reference to theaccompanying drawings in which:

FIGURE 1 is a longitudinal section elevational view of the transitionstructure of the invention;

FIGURES 2A-2G are successive cross-section views of the structure ofFIG. 1 including representations of the electric fields.

FIGURE 2D is a cross-section view taken at 2D showing the electric fieldof an undesirable TE mode;

FIGURE 2D" is a cross-section view taken at 2D illustrating the additionof a radial vane or ridge for eliminating the undesirable TE mode; and

FIGURE 3 is a partially broken away perspective view of the transitionstructure of the invention.

Referring to FIGS. 1 and 3, the illustrated embodiment of the transitionstructure of the invention is formed of three conuctive membersincluding a section of rectangular waveguide 10, a section of circularwaveguide 11 and a transition member 12.

FIGS. 2A-2G are succesive cross-sections of the structure of FIG. 1showing development of the transition member 12 and the gradual changeof the TE mode in the rectangular crosssection of FIG. 2A to the TEcircular mode in the circular cross-section of FIG. 2G.

As shown in FIG. 2A the rectangular waveguide section 10 has arectangular cross-section of dimensions suitable for propagating theinput electromagnetic wave in the TE rectangular mode at the frequencyof interest. A single arrow represents the electric field, it beingwell-known that the TE mode in a rectangular waveguide has a transverseelectric field parallel to the narrow walls which varies from a maximumintensity at the center of the waveguide to a minimum intensity at thenarrow walls.

As best shown in FIG. 1, a right hand portion 14 of the upper narrowwall of rectangular waveguide section 10 is gradually formed into anarcuate shape so that at cross-section 2B this arcuate shape matches thecurvature of the inside circumference of the circular waveguide 11. Thusas shown in FIG. 2B the transition waveguide channel shape atcross-section 2B is rectangular with an arcuate upper narrow wall.

Between cross-sections 2B and 2D the transition waveguide channel shapeevolves from rectangular to semi- 3 circular, the electric fieldchanging correspondingly as shown by the electric field arrows of FIGS.2B-2D. In effect, the broad walls of the rectangular shape of FIG. 2Bare pivoted at their junctions with the lower narrow wall at a uniformrate until they become collinear with the lower narrow wall whereby thesemicircular crosssection of FIG. 2D is obtained.

Between cross-sections 2D and 2G the waveguide shape evolves fromsemicircular to the full circular shape of circular waveguide 11. Ineffect, this is accomplished by pivoting the equal halves of thestraight wall of the semicircular shape (FIG. 2D) at its center at auniform rate until these two halves terminate in a vertical knife edge(FIG. 2F). This completes the transition and the electric field linesare now formed in the concentric circles of the TE circular mode, theelectric field of the TE mode having no radial components and having anintensity which varies from maximum at one-half wave-guide radius tominimum at the center and at the wall of the circular waveguide. (Theinside diameter of circular waveguide section 11 is selected, inwell-known manner, for propagation in the TE mode at the frequency ofinterest.)

While the rectangular to circular waveguide transition as describedhereinbefore has been found relatively free of conversion to undesirablemodes, there is the possibility of the excitation of an unwanted TEcircular mode in particular. Representative electric field lines of theTE mode in the semicircular cross-section are shown in FIG. 2D. This TEmode may be substantially eliminated, without disturbance of the TEmode, by providing the previously mentioned radially-positioned narrowconductive ridge shown as a ridge 13 in FIG. 2D" positioned to bifurcatethe waveguide channel of the transition structure. The ridge 13 mayextend the entire length of the transition structure or a lesser portionthereof as required. (To maintain clarity of the drawing the ridge 13 isnot shown in FIGS. '1 and 3.) The ridge 13 terminates the electric fieldlines of the TE mode thus providing substantial suppression thereof.

Construction of the described rectangular to circular waveguidetransition is relatively simple compared to prior devices of this type.The transition member 12 may be separately machined from solid roundstock and then inserted into the circular waveguide section 11. Thearcuate portion 14 is similarly separately machined in the upper narrowwall of rectangular waveguide before attachment, by means of suitableflanges, to the assembled circular waveguide section 11 and thecontained transition section 12. The ridge 13 may conveniently besupported in a longitudinal slot (not shown) machined in the wall of thecircular waveguide 11.

Representative dimensions of a rectangular to circular waveguidetransition according to the invention constructed for operation at Kband (166s) are as follows: the rectangular waveguide section 10 hadinside dimensions of 0.510" by 0.255", the length of the portion 14(transition to arcuate shape) being 0.540". The circular waveguidesection 11 had an inside diameter of 1.090". The transition member 12had a length of 13", the crosssections 2B-2F being equally spaced. Theridge 13 may 4 have a thickness of .040, and a length of at least 9" asmeasured to the left from cross-section 2F.

While the invention has been described in terms of a rectangular tocircular waveguide transition, it is noted that the described structurecan also be employed in the reverse direction for transition of anelectromagnetic input wave in the TE mode in the circular waveguide to aTE mode in the rectangular waveguide.

Thus what has been described is a relatively simple wideband, low-lossmode transition structure.

While the principles of the invention have been made clear in theillustrative embodiments, there will be obvious to those skilled in theart, many modifications in structure, arrangement, proportions, theelements, materials, and components, used in the practice of theinvention, and otherwise, which are adapted for specific environmentsand operating requirements, without departing from these principles. Theappended claims are therefore intended to cover and embrace any suchmodifications within the limits only of the true spirit and scope of theinvention.

What is claimed is:

1. A transition device between a rectangular waveguide having broad andnarrow walls of predetermined transverse length and a circular waveguidehaving a predetermined radius, comprising: a first rectangular portionwherein one narrow wall is changed to an arcuate narrow wall over apredetermined longitudinal length, said arcuate narrow wall having aradius equal to the radius of said circular waveguide; a second portionof predetermined longitudinal length over which the internalcross-section area is increased by gradually increasing thecircumferential length of said arcuate wall by pivoting said broad wallsat their junctions with the other narrow wall to thereby form asemicircular cross-section at the end of said second portion; and athird portion of predetermined longitudinal length over which theinternal cross-section area is gradually further increased by graduallyfolding at the center thereof the two halves of the straight wall ofsaid semicircular cross-section until said two halves coincide in aradially extending knife edge at the end of said third portion, and aradially extending conductive ridge positioned to substantiallybifurcate the length of the third portion of said transition device,whereby an undesirable TE mode is suppressed.

2. The transition device defined by claim 1 wherein said longitudinallengths of said second and third portions are equal.

3. The transition device defined by claim 1 wherein said changes incross-section shape of said first and second waveguide portions occur ata longitudinally uniform rate.

References Cited UNITED STATES PATENTS 2,656,513 10/1953 King 333-212,779,923 1/1957 Purcell 33321 2,810,890 10/1957 Klopfenstein 33373 ELILIEBERMAN, Primary Examiner. HERMAN KARL SAALBACH, Examiner. RONALD D.COHN, Assistant Examiner.

1. A TRANSITION DEVICE BETWEEN A RECTANGULAR WAVEGUIDE HAVING BROAD ANDNARROW WALLS OF PREDETERMINED TRANSVERSE LENGTH AND A CIRCULAR WAVEGUIDEHAVING A PREDETERMINED RADIUS, COMPRISING: A FIRST RECTANGULAR PORTIONWHEREIN ONE NARROW WALL IS CHANGED TO AN ARCUATE NARROW WALL OVER APREDETERMINED LONGITUDINAL LENGTH, SAID ARCUATE NARROW WALL HAVING ARADIUS EQUAL TO THE RADIUS OF SAID CIRCULAR WAVEGUIDE; A SECOND PORTIONOF PREDETERMINED LONGITUDINAL LENGTH OVER WHICH THE INTERNALCROSS-SECTION AREA IS INCREASED BY GRADUALLY INCREASING THECIRCUMFERENTIAL LENGTH OF SAID ARCUATE WALL BY PIVOTING SAID BROAD WALLSAT THEIR JUNCTIONS WITH THE OTHER NARROW WALL TO THEREBY FORM ASEMICIRCULAR CROSS-SECTION AT THE END OF SAID SECOND PORTION; AND ATHIRD PORTION OF PREDETERMINED LONGITUDINAL LENGTH OVER WHICH THEINTERNAL CROSS-SECTION AREA IS GRADUALLY FURTHER INCREASED BY GRADUALLYFOLDING AT THE CENTER THEREOF THE TWO HALVES OF THE STRAIGHT WALL OFSAID SEMICIRCULAR CROSS-SECTION UNTIL SAID TWO HALVES COINCIDE IN ARADIALLY EXTENDING KNIFE EDGE AT THE END OF SAID THIRD PORTION, AND ARADIALLY EXTENDING CONDUCTIVE RIDGE POSITIONED TO SUBSTANTIALLYBIFURCATE THE LENGTH OF THE THIRD PORTION OF SAID TRANSITION DEVICE,WHEREBY AN UNDESIRABLE TE11 MODE IS SUPPRESSED.